R&D Report 1993-13 : The development of the switched-horn radio-camera system
R.H. Evans, C.E. Melvin, J.T. Zubrzycki
Radio-cameras are now well established at outside broadcast events (OBs) but conventional circularly polarised antennas and electromechanical tracking systems still leave considerable room for improvement. A new radio-camera system is described which uses a cluster of six directional transmitting antennas, with each antenna pointing in a different direction. Test signals inserted into the video during the field blanking interval are transmitted through each antenna in turn, and are then analysed at the receiving base station to determine which horn is transmitting the best signal. The result of this analysis is used to select the best horn for the following frame of video, and the result is updated 25 times each second. Both the level of the received signal strength and the degree of multipath distortion are analysed to determine the best horn.
This report describes the development of a prototype switched-horn system and also describes two field trials, one of which took place during a live programme transmission. The results of the trials showed that the switched-horn system suffers from far less multipath distortion than conventional omnidirectional circularly-polarised antennas, and does not have any of the drawbacks of electromechanical systems.

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